Reflex Cardiovascular Responses to Cold Exposure of the Face or Foot

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Abstract
Subjects (6) performed a breathholding maneuver during facial cooling and immersed their foot in cold water, without drugs and after the i.v. administration of propranolol plus atropine (P+A). Cardiac interval (INT), mean interval for longest consecutive 5 cycles (L5INT/5); systolic time intervals including electromechanical systole (EMS), left ventricular ejection time (LVET), pre-ejection period (PEP) and PEP/LVET; and systolic (SP) and diastolic pressures (DP) were monitored during supine rest, during apnea with a plastic bag of ice water on the face, and from 16-30th and 46-60th s of 1-min periods of foot immersion in 4.degree. C water. P+A administration induced reduction in INT, L5INT/5, and LVET and increase in PEP, PEP/LVET and DP. INT, L5INT/5, PEP, SP and DP increased during facial cooling without drugs. Only the increases in INT and L5INT/5 were abolished by P+A and probably from reflexes mediated by vagal or sympathetic outflow to the heart. Reductions in INT, L5INT/5, EMS, PEP and PEP/LVET at 16-30 s of foot immersion without drugs were not observed after P+A; 40-60 s responses neared resting values with and without P+A. An initial cardiac reflex response to foot immersion may be overpowered by the ventricular afterload and the baroreceptor response due to the increased arterial pressure.